Drying time and curing time are different. Drying time, the time it takes to be able to handle the parts, is generally only a few minutes. Curing time, the time it takes the paint to completely cure, is significantly longer. Acrylics do not adhere to the surface in the same way that enamels and laquers do and if they are not completely cured (and frequently even if they are) they will pull loose when masked.
I frequently spray subsequent coats, even other colors, after 30 to 60 minutes of drying time. IF you have to mask it, wait at least 24 hours. If you have to spray enamel or laquer over it, wait at least 24 hours and even then sray the first couple of coats very, very lightly.
I haven't noticed that temperature has a large affect on the drying time, at least within reason. My basment is usually pretty cool and they still dry to the touch very quickly. Humidity, however, does have an affect on how long they take to dry and cure.
A word of warning if you haven't used acrylics much; THOROUGHLY clean the parts prior to painting. Acrylics do not have the chemical solvents in them that enamels or laquers do and usually cannot dissolve any oil or grease that is on the surface. Additionally, priming of the parts is more critical with acrylics than with enamel or laquer for the same reason. They just do not adhere as well as enamel or laquer.